The broad and long-term objectives of this proposal are to understand the roles played by the TIE2 receptor and its ligands, angiopoietins, in cardiovascular development, and to gain insights into the molecular mechanisms by which the TIE2 receptor and angiopoietins regulate cardiovascular development. The cardiovascular system is one of the earliest organ systems to develop in our bodies. Normal development and physiological functions of other organs are critically dependent on the normal functioning of the cardiovascular system. In past years, a number of genes that critically regulate the development of both cardiac and vascular systems have been identified. However, in the cardiac systems, the primary focus has been on the morphogenesis and physiological functions of myocardium. Mechanisms of the formation of endocardium have been relatively under appreciated. Furthermore, very little is known about the mechanisms by which endocardium affects the development of the myocardium, although the importance of this type of cross-talk of the two cardiac systems has been known. The specific aims of this proposal are: 1) To test the hypothesis that angiopoietin-1 and angiopoietin-2 cooperatively regulate the activity of TIE-2 receptor and other novel receptors to control the formation of endocardium; 2) To test the hypothesis that normal formation of endocardium, as a feedback mechanism, controls the normal development of myocardium; 3) To test the hypothesis that angiopoietins and VEGF cooperatively control the formation of endocardium; 4) To test the hypothesis that angiopoietins and TIE receptors control the formation of endocardium by regulating the Akt intracellular signaling pathway; and 5) To test the hypothesis that the Akt intracellular signaling pathway is involved in murine models for human cardiac malformation diseases. The investigators will accomplish these goals by extensive use of null and conditional knockout mice, novel transgenic-based indicator and reporter systems, state-of-the-art gene cloning, and expression analyses. Upon the completion of these projects the investigators hope to be able to gain new molecular insights into the mechanisms of endocardial morphogenesis, an area of research that is at an early stage. Furthermore, they will be able to gain molecular insights into cross-talk between endocardium and myocardium during the cardiac development. Studying these basic molecular mechanisms of cardiac morphogenesis is expected to contribute to a future development of effective therapeutics for a number of human cardiovascular diseases.